1. Field of the Invention
The present invention relates to a technique of determining whether an image on an output (recording medium) delivered from an image forming apparatus is non-defective or not.
2. Description of the Related Art
In recent years, with an increase in the range of use of image forming apparatuses, such as copying machines, the reliability of images formed thereby on the recording media, such as sheets, has come to be considered increasingly important. For example, a plurality of images based on the same image of an original (original image) have come to be more often recorded (formed) on a plurality of recording media, not only for internal use thereof within a company, but also for external use thereof outside the company. In such a case, it is regarded essential that all the images formed on the recording media are accurate copies of the original image.
An inaccurate copy of the original image is, for example, a defective image formed such that it bears a toner at a location which should be a surface of a recording medium.
To overcome such a problem, an inspection technique becomes necessary which detects recording media having such defective images formed thereon. Further, in the inspection, from the viewpoint of productivity, it is required to detect defective images at high speed.
It should be noted that Japanese Laid-Open Patent Publication (Kokai) No. H05-022593 discloses a technique of quickly discriminating a read image from a particular image, such as the image of a currency note. In this technique, higher five bits of an 8-bit signal indicative of a pixel value of each of RGB colors read in by a CCD are used to perform the discrimination.
According to the technique disclosed in Japanese Laid-Open Patent Publication (Kokai) No. H05-022593, as a signal for use in discriminating a read image from a particular image, such as the image of a currency note, there is employed a signal formed by dropping the lower bits of the 8-bit signal, as mentioned above. Therefore, according to the disclosed technique, by dropping the lower bits, details of information on the read image are lost. This can undesirably cause an overlook of a very small defect during inspection of the recording media.
From the view point of inspection accuracy, it is desirable to perform inspection using all bits of the signal indicative of a pixel value of each of RGB colors. In this case, however, the speed of inspection becomes lower.